Process for refining mineral oils



Jan. 10, 1939. A. P. ANDERSON PROCESS FOR REFINTNG MINERAL OILS Filed March 27, 1936 Patented Jan. 10, 1939 PATENT OFFICE PROCESS FOR DEFINING MINERAL OILS Alvin P. Anderson, Alton, 111., assignor to Shell Development Oompany, 8an Francisco, Calif, a corporation oi Delaware Application March 27, 1936, Serial No. 71,19!

11 Claims.

This invention relates to the refining of mineral lubricating oils, and is particularly concerned with a process for the acid treatment of highly parafiinic oils which it is difilcult to refine by the known sulfuric acid treating methods.

Mineral oils used for lubrication are often subjected to treatment with sulfuric acid during processing to decrease their tendencies to discolor and to form sludge and other undesirable products. These undesirable, unstable components are normally present but are removed by the acid. Diiierent methods of applying the acid to the stock treated have been developed to obtain economies or operating advantages. The most common methods are the direct mixing under optimum conditions in batch agitators or continuous mixers and settling the resulting sludge in the agitator or in separate settlers, and to mix the acid with suitable mechanical mixers and then to remove the sludge by centrifuging.

There are oils, however, that contain these unstable materials but which cannot be acid treated by the normal procedures because the sludge particles are too finely dispersed forming so-called pepper sludge which cannot be removed by ordinary means. These oils are highly parafiinic in nature and comprise oils distilled from certain Pennsylvanian crudes and oils produced by selective extraction with solvents in such a way that the paraflinic portion (raflinate) which is to be finished to produce lubricating oils has a viscosity index (Dean and Davis) higher than about '70 or 80. The viscosity index is a measure of paraflinicity and is described in Chemical and Metallurgical Engineering 1929, vol. 36, No. 10, page 618 (Viscosity Variations of Oils with Temperature, by E. W. Dean and G. H. B. Davis). Highly paraifinic oils such as Pennsylvanian may have viscosity indices of approximately one hundred, while naphthenic oils may have zero or negative viscosity indices.

The practice with such oils is to treat with clay alone in sufiicient quantities to obtain the desired color, etc- As faras I know, no generally satisfactory method of acid treating such oils with sulfuric acid has been revealed. It is known that very small amounts of acid, two to three pounds per barrel, or that very large amounts of acid, fifty to sixty pounds per barrel, can be applied successfully. These amounts are either too small toeflfect any, appreciable savings in clay or too large to be economical except for certain high priced oils forspecial purposes.

The objectofthis invention is to provide a simple but effective means of acid treating paraffinic stocks with any amount of acid desired to effect savings in clay and to increase the stability of the finished oil. In accordance with the present invention it has been found that small quantitles of the extract (naphthenic portion from solvent extraction) and unsaturated asphaltic materials are very eflective as coagulating agents and that with their aid paraflinic oils can be readily acid treated by otherwise normal methods. These materials can be employed separately or together.

My invention may be further understood by referring to the accompanying drawing, which is a schematic flow diagram illustrating one embodiment of my invention.

In the drawing, i and 2 are mixing and agitating devices; 3 is a settling tank adapted for the separation of immiscible liquids; l is an extraction apparatus, which may be a series of mixers and settlers, or a contact tower provided with means for the countercurrent flow of liquids; 5 and 6 are continuous settlers, adapted to separate acid sludge from oil; I, 8, 9 and in are separating apparatus, such as combinations of evaporating and distilling units; II is an apparatus for clay treatment; i2 and I3 are condensers; and l4, l5 and ii are storage tanks for a selective solvent, naphtha, and sulfuric acid, respectively; all interconnected as shown as hereafter described, and provided with pumps, flow control devices, heat exchangers, and other auxiliary equipment, not shown.

My process will first be described as applied to the treatment of an oil containing a sumcient quantity of hydrocarbons of low viscosity indices to necessitate its extraction with selective solvent to improve its temperature-viscosity characteristics. In this type of process, the initial mineral oil fraction is introduced into the extraction apparatus 4 through a conduit i1 and valve i8, and extracted therein with a selective solvent for aromatic or naphthenic oils, such as liquid sulfur dioxide, furfural, pp dichloroethyl ether, cresol, phenol, nitrobenzene or any other equivalent selective solvent or mixture of solvents such as a mixture of sulfur dioxide and benzol or kerosene extract supplied from the tank l4 through a valve IS. The liquid raflinate and extract phases produced in the extraction apparatus are withdrawn at 20 and 2|, respectively, and treated in the apparatus 8 and 9 to recover the selective solvent, which is condensed and returned to the tank II. The extracted raihnate oil is withdrawn at 22 and the extract at 23.

The rafiinate oil is next flown through a valve 24 and intimately mixed with a proper quantity of concentrated sulfuric acid in the mixer 2. The concentration of the acid may be varied to suit the viscosity of the oil, and may, for example, be between 85 and 100% and will generally be higher than 90% for the more viscous oils. Moreover, it may often be desirable to employ fuming sulfuric acid, as for example, oleum, particularly in the refining of viscous white oils. The quantity of acid will also vary with the stock being treated, and may, for example, be between live to fifty pounds of 66 36. acid per barrel (42 U. S. gals.). The temperature of the agitation may, for example, be between 10 C. and 60 C., but my process is not restricted to these limits.

The contacting of the acid and oil in the mixer 2 may be effected with air; or the mixer 2 may be provided with a propeller and draft tube. After the acid has acted on the impurities in the oil, the mixture of oil, acid and sludge is fed through a conduit 25 to the settler 5, the sour oil overflowing the conical settling chamber into the peripheral launder 26, and being withdrawn through valves 21 and 28 for further treatment, such as dewaxing or neutralization with soda or clay treatment. If clay treatment is to be employed the sour oil is introduced into the apparatus II where it is contacted with clay, pref erably at an elevated temperature above about 140 0., but below cracking temperature, the flnished oil being withdrawn at 29.

The acid sludge is continuously pumped from the bottom of the conical settler 5 and discharged at 30.

The acid treatment can in many cases be carried out more readily by diluting the oil with a light distillate, such as propane. gasoline, naphtha or a similar hydrocarbon distillate. This is particularly desirable when it is desired to dewax the oil in its diluted state following the acid treatment. For this purpose, the diluent may be supplied from the tank l5 through a valve 3|. If desired, the diluent may be recovered from the sour oil prior to clay treatment by means of the apparatus III. A further economy from the use of the diluent arises from the possibility of improving the yield by washing the acid sludge to recover entrained oil. This may be eii'ected by feeding the acid sludge and the diluent through valves 32 and 33 into a mixer 34, and separating the resulting mixture in the settler 6, the diluent with dissolved oil being recycled through the valve 35 and the sludge withdrawn at 36.

It is moreover, in many cases desirable to acid treat the raflinate oil in the presence of dissolved selective solvent. such as sulfur dioxide. In this case, the separating apparatus 8 may be eliminated, and the raflinate phase from the extraction apparatus 4 fed into the mixer through by-pass valve 31.

As was pointed out above, when the rafllnate oil which is treated with acid has a viscosity index greater than about '70 or 80, it is often diflicult to remove the sludge from the oil'in the settler 5. In accordance with the present invention, I overcome this diificulty by introducing a small amount of the aromatic extract into the oil. This extract is herein designated as S02 soluble", although it may be obtained with the aid of any similar selective solvent. Between 1 and 10% of this extract based on the weight of oil to be acid treated are generally suflicient, altho I am not restricted to this exact range.

To introduce the S02 soluble extract, I mayopen the valve 38, so as to cause a portion of the extract oil to flow through the conduit 39 into the mixer 2. It should be noted that the amount of extract thus introduced is not suflicient to impair the viscosity index of the flnal product to any marked degree; nor is the addition of this extract equivalent to operating the extraction apparatus 4 in a manner to remove a smaller quantity of extract, because the components of the oil which are particularly effective in improving the separation of the acid sludge in the settler 5 are those which are the most soluble in selective solvents, and would for this reason be removed from the oil altho a smaller amount of selective solvent were employed in the extraction.

It is also possible to concentrate the most soluble components of the oil by subjecting the extract flowing through the conduit 2| to a treatment for the separation of the less soluble hydrocarbons. Thus, the initial extract in the conduit 2i may be chilled to cause the formation of two secondary liquid phases, the hydrocarbons which remain dissolved in the selective solvent, or a portion of them fed through the conduit 39; or a portion of the selective solvent may be separated by distillation, and the resulting solvent-poor extract phase chilled to cause a similar separation into secondary liquid phases.

According to an alternative method of concentrating the most soluble components of the oil, all or a portion of the initial oil may be fed to the mixer I through a valve 40 and mixed with selective solvent, fed through a valve 4|. The

.- resulting mixture is transferred to the settling tank 3, where the mixture is permitted to stratify, the oil phase being removed through tlm conduit 42, and the extract being withdrawn at 43 and treated in the apparatus 1 to recover the selective solvent. The quantity of the solvent supplied through the valve 4| is preferably small, and the temperature is such that only a small amount of the extract phase is formed, the greater part of the oil being thereby withdrawn as the oil phase. In this manner only the most soluble components are dissolved in the extract phase, and the operation of the apparatus 4 is not adversely affected, since only suflicient oil is preferably passed through the valve 40 to provide the desired quantity of SO: soluble extract for admixture with the oil to be acid treated, the bulk of the 011 being fed into the apparatus 4 through the .valve it. The S0: soluble extract from the apparatus 1 is introduced into the mixer 2 through conduits 44 and 39, as described above.

When it is desired to acid treat an oil which is initially highly parailinic, and required no extraction, this oil may be introduced into the process through a conduit 45 and valve 46, and the S02 soluble extract may be introduced into the oil from an outside source; it may be supplied by extracting an oil of low paramnicity with a selective solvent in the manner heretofore described, closing the valve 24, withdrawing the raflinate oil at 41, and utilizing the extract for admixture to the paraflinic oil which is supplied at 45.

To illustrate the process further, and to demonstrate the benefits to be derived from my process, the following example is given:

Example-A Mid-Continent lubricating oil was extracted with iurfural to produce a dark colored rafflnate oil having a viscosity index of 95 and a contacted Acid treated with 15% and contacted activated with 5% act:-

clay vated clay Color, N. I. A 5+ 5+ Visa, sec. Say. Univ. at 2l0 F 151- Stability towards oxidation? Vise. sec. Say. Umv. at 210 F.

after- 80 175 155 168 hrs 230 106 Determined according to method outlined in National Petroleum News, 1933, vol. 25, No. 37. page 27 (Effect of Sludge on Engine Oil Performance. by Bernard, Rogers, Shoemaker and wllklll).

From the above table it is apparent that acid treating in the manner previously described saves a considerable quantity of clay and improves the stability towards oxidation to a marked degree. Ordinarily, extraction solvents remove unsaturates and aromatics of the type soluble in liquid sulfur dioxide. Acid treating with sulfuric acid removes other unstable compounds insoluble in the selective solvents, or not sufliciently soluble therein to be effectively removed thereby, and consequently increases the stability of the oil.

My invention may be applied to oils of any viscosity, but is particularly effective to the more viscous oils, such as those having viscosities higher than 80 seconds Say. Univ. at 210 E, which are particularly difiicult to treat with the known methods. I have found it preferable to employ an $02 soluble extract which has approximately the same viscosity as the oil being acid treated, so that the viscosity of the final product is not influenced by the viscosity of those portions of the added extract which are not removed with the acid sludge. Asphaltenes and asphaltic resins precipitated from oils containing them by means of light hydrocarbons such as propane, butane, naphtha, etc., or asphaltic materials obtained as distillation residues can also be used in addition to or in place of the above described S02 soluble extract.

I claim as my invention:

1. A process for refining lubricating oils, comprising the steps of extracting a lubricating oil containing paraflinic and non-paraifinic hydrocarbons with a selective solvent for non-parafiinic hydrocarbons under conditions causing the formation of a relatively small quantity of a first extract oil and a relatively large quantity of a first rafiinate oil, further extracting the rafiinate oil with a selective solvent of the same type to produce a second rafiinate oil having a viscosity index greater than about '70, and a second extract oil, contacting the second raifinate oil with a concentrated strong mineral acid in the presence of at least a portion of the first extract oil, thereby forming an acid sludge, and separating the acid sludge from the sour oil.

2. The process according to claim 1 in which the first rafiinate oil is mixed with an additional quantity of unextracted oil before being further extracted to produce the second raflinate oil.

3. In theprocess of refining a highly paraffinic lubricating oil having a viscosity index greater than about 70, which upon treating with concentrated sulfuric acid produces pepper sludge not removable by settling, the improvement comprising adding to the said parafiinic oil a small quantity of a sulfur dioxide soluble mineral oil having approximately the same viscosity as the paraflinic oil, and treating the resulting mixture with concentrated sulfuric acid, thereby forming a sludge capable of settling.

4. The process according to claim 3 in which the initial oil has a viscosity of over 80 seconds Saybolt Universal at 210 F.

5. The process according to claim 3 in which the quantity of the extract is between 1 and 10% of the initial oil.

6. In the process of refining lubricating oils containing paramnic and non-paramnic hydrocarbons by solvent extraction to produce a parafflnic raflinate and a non-parafllnic extract oil, said raflinate having a viscosity index greater than about 70 and producing upon treatment with concentrated sulfuric acid a pepper sludge not removable by settling, the improvement comprising returning a portion of the extract oil to the said raflinate and treating the resulting mixture with concentrated sulfuric acid, thereby forming a sludge capable of settling.

'7. A process for refining lubricating oils comprising the steps of extracting a lubricating oil fraction containing paraflinic and non-paraflinic hydrocarbons with a selective solvent for nonparaflinic hydrocarbons to. produce a raffinate having a viscosity index greater than about 70 and an extract oil, further treating said extract oil to separate it into two fractions which, relative to each other, are more and less soluble in the selective solvent, and contacting the raffinate oil with concentrated sulfuric acid in the presence of at least a portion of the more soluble extract fraction, thereby producing an acid sludge, and separating the acid sludge from the sour oil.

8. In the process of refining a highly paraffinic lubricating oil having a viscosity index greater than about 70, which upon treating with concentrated sulfuric acid produces pepper sludge not removablebysettling,theimprovementcomprising adding to the said parafiinic oil a sulfur dioxidesoluble mineral oil having approximately the same viscosity as the paraflinic oil in an amount insuificient materially to impair the viscosity index of the latter, and treating the resulting mix- .ture with concentrated sulfuric acid, thereby forming a sludge capable of settling.

9. In the process of refining a highly paraffinic lubricating oil having a viscosity index greater than about '10, which upon treating with concentrated sulfuric acid produces pepper sludge not removable by settling, the improvement comprising adding to the said paraflinic oil a sulfur dioxide-soluble mineral lubricating oil in an amount insufficient materially to impair the viscosity index of the parailinic lubricating oil, and treating the resulting mixture with concentrated sulfuric acid, thereby forming a sludge capable of settling.

10. Inthe process of refining a highly paraffinic lubricating oil having a viscosity index greater than about 70, which upon treating with concentrated sulfuric acid produces pepper sludge not removable by settling, the improvement comprising adding to the said paraflinic oil a sulfur dioxide-soluble mineral lubricating oil in an amount insufiicient materially to impair the viscosity index of the parafiinlc lubricating oil and 75 sludge, with non-fuming sulfuric acid, which comprises agitating the oil with concentrated sulfuric acid in the presence of an added normally liquid unsaturated cyclic hydrocarbon in amount of from 1 to 10% of the oil, and separating the 5 sludge formed from the oil.

. ALVDT P. ANDERSON. 

